Jennifer Thalasinos lay motionless across the altar steps, her head and upper body covered by a white prayer shawl. Around her, the Shiloh Messianic congregation, eighty or ninety strong, sang and prayed. Worshippers turned toward Jerusalem, their arms raised. The pastor, Bruce Dowell, strummed a guitar and, in a warm baritone, sang, “These are the final days.” The shawl that covered Thalasinos had belonged to her husband, Nicholas. He and thirteen others were killed by gunfire in the December 2nd attack on a county workers’ holiday party in San Bernardino, California.

Nicholas Thalasinos was fifty-two. He was a restaurant inspector who, according to his widow, loved Godzilla—he once took his two sons to a Godzilla convention in Chicago. Raised in New Jersey, Thalasinos had been a county health inspector in Cape May, and a member of a Greek Orthodox church in North Wildwood, before moving to California in 2002. He and Jennifer, who teaches second grade, liked to watch the Food Network, particularly cooking-competition shows. A few years ago, they joined Shiloh Messianic. Its members study both the Torah and the Bible, with the aim of uniting Judaism and Christianity. They take their inspiration from Paul, in Ephesians: “Joining Jew and Gentile together as One New Man.” Nicholas became a deacon. At his office, he was known for his red suspenders, bright button-down shirts, and fedora. He liked to think of himself, Jennifer told me, as “the gentleman inspector.”

“Keep Torah, and you will succeed in all that you do,” Pastor Dowell intoned. Jennifer Thalasinos had returned to a front-row seat. She still had the prayer shawl over her head and shoulders. All the women wore head scarves of some kind. The building wasn’t actually a church but a rented space in Calimesa, a small city in the foothills of the San Bernardino Mountains, seventy miles east of Los Angeles. Just across a frontage road, Interstate 10 rumbled with Saturday-morning traffic. It had been exactly a month since the attack. “We will be reunited,” the pastor promised from the stage.

But the service, a Shabbat, was more rocking and joyous than condolatory. A drummer and two electric guitarists drove most of the songs, with lyrics projected high above the altar, while women danced, holding hands in a circle. Men prostrated themselves on the floor. This was charismatic worship, and there were meet-your-neighbor intervals where big men embraced me and women touched my face, looked into my eyes, and asked me what I was searching for. A sweet-smelling grandmother asked where I was from, laughed when I told her New York, and said that she was a “Jewish American princess” from Long Island. There was an abundance of praise of Yeshua, and much passionate, less than fluent Hebrew.

“It’s like a marriage, like husband and wife,” Pastor Dowell had told me. “Nicholas fit right in. He had just discovered, or concluded, that he was Jewish. He was growing in the Lord, growing in his spiritual walk. He became an important servant in the congregation. He was thrilled to be here. Everybody knew where Nick went to church. He had come home.”

Dowell’s sermon was relaxed and funny, at his own expense, but also apocalyptic. “Today is very much a warfare message,” he said. “We’re preparing for battle. Prepare for whatever the enemy may throw at you this year.” He gave practical advice. “Don’t get tattoos—your body is a temple, not a scratch pad.” For some of his members, the advice was too late. But Dowell’s main theme was strife and reckoning. “There are two bloodlines running through the world,” he said. “So there’s going to be a fight. Where we’re going, the apostasy is going to be great. Do you believe in the Last Days?”

“Yes!”

“Then the apostasy is going to be great.” Dowell spoke about “the battlefield of Armageddon, where the blood is going to run as deep as the horse’s bridle.”

After the service, I sat with Jennifer Thalasinos. She is soft-spoken, pale-skinned, forty-one. She wore large-framed glasses. Her eyes are green. She and Nicholas had been married nine years. It was his second marriage. He had been an extraordinarily gentle man, she said, and a serious student of the Bible. “I have his iPad,” she said. “He took an incredible number of notes, literally thousands, all Biblical.” The couple had renewed their marriage vows last winter. Nicholas had been in a rush to do so. “He said he felt like something dark would happen. He was preparing for Armageddon, or whatever was coming.” She added, “We’re preppers, from even before he was saved.”

After joining Shiloh, Nicholas, who described himself as a Messianic Jew, wore tzitzit, the knotted tassels sometimes worn by observant Jews, and a Star of David tie pin. He had been confronted once by an anti-Semite in a parking lot. “Nick was very outspoken about his faith,” Jennifer said. “But we agreed we were going to stay strong. I wear my Star of David all the time, and it has the Cross in it, which makes it even more controversial.” Jennifer had belonged to an evangelical megachurch in Colton, her home town, which borders San Bernardino to the south, before she and Nick began worshipping at Shiloh Messianic. “We just found out, through ancestry.com, that we’re both part-Jewish,” she said.

Jennifer believes that her husband was one of the principal targets of the December 2nd attack. He had been particularly outspoken—vitriolic, really—about his beliefs on Facebook and Twitter, and he had been arguing about religion in the preceding weeks at his office with another county health inspector, Syed Rizwan Farook. In an irony too grotesque to unpack, Thalasinos had refused to agree with Farook, a devout Muslim, when Farook insisted that Islam is a religion of peace. Farook and his wife, Tashfeen Malik, were, of course, the two attackers. Jennifer did not know for certain that their rifle fire was concentrated on her husband. No forensic report has been released, and she chose not to go to a debriefing held by the F.B.I. for the families of the fourteen dead. “A woman who was wounded contacted me, and she told me that my husband, who was already mortally wounded, told her to get under the table,” Jennifer said. “She thinks that he saved her life. That was all I needed to know.” Nicholas had spoken to her about Farook, Jennifer said, but he hadn’t seemed wary of him. “I knew Nick and Syed talked. I knew Nick tried to bring him to Christ several times.”

Why did the attack happen? Farook and Malik did not make a martyr video or leave a manifesto. They didn’t wear suicide vests or scream “Allahu akbar” when they opened fire. Malik did post to Facebook a short, garbled, last-minute shout-out to the leader of the Islamic State. But their families, neighbors, former classmates—and, in Farook’s case, colleagues and fellow-worshippers—expressed only astonishment after the attack. There had been no displays of anger, no indication. Only growing piety.

Farook, born in Chicago to Pakistani immigrants, grew up in the sprawling, sunny suburbs of Riverside, just southwest of San Bernardino. Malik, born in Pakistan, had been raised largely in Saudi Arabia, where her father was an engineer. She earned a degree in pharmacology in Pakistan in 2012, met Farook on a matrimonial Web site called BestMuslim.com, married him, and moved to the United States in 2014. A daughter was born in May, 2015. He was twenty-eight and she twenty-nine when they died in a storm of police gunfire after a car chase.

Then surfaced the strange tale of Enrique Marquez, Jr. In 2004, his family moved in next door to the Farooks on Tomlinson Avenue, in Riverside. Marquez was fourteen, lonely, struggling. He started hanging out with Farook, who was eighteen, tall and shy, and worked on cars in his driveway. Marquez became the older boy’s acolyte. Neither of them seems to have had other friends. Farook taught Marquez motor mechanics, and introduced him to Islam. In 2007, at sixteen, Marquez converted. Farook prayed with him. Soon after, he turned him on to the sermons of Anwar al-Awlaki, the American-born imam who had joined Al Qaeda in the Arabian Peninsula. Together, they read Inspire, the Al Qaeda magazine, and other jihadist literature online. Farook confided that he was considering going to Yemen to join Al Qaeda.

Awlaki was, to a certain cast of mind, a mesmerizing preacher. This world is but a station, he proclaimed. It is the next station, the Hereafter, that matters. “We do not belong here. We are travelling. . . . We need to prepare for death.” Awlaki called for jihadists in the West to attack soft targets, particularly in the United States, and many took inspiration from him, including the London Tube and bus bombers (2005); Major Nidal Malik Hasan, the Army psychiatrist, who killed thirteen and wounded dozens at Fort Hood, Texas (2009); Umar Farouk Abdulmutallab, the airline underwear bomber (2009); Faisal Shahzad, the Times Square van bomber (2010); and the Tsarnaev brothers, who carried out the Boston Marathon bombing (2013). An American drone strike killed Awlaki in Yemen in 2011, but his message continues to resonate through the Internet. A recent issue of Inspire reprints his work, again stressing that it is best for the believer “to perform his duty of Jihad in the West.”

Inspire, like much of the Islamic State’s propaganda, is directed at disaffected youth. Across a double-page photograph of a brooding young man in a dark room is a caption in verse:

For how long will you live in tension?

Instead of just sitting, having no solution,

Simply stand up, pack your tools of destruction.

Assemble your bomb, ready for detonation.

That issue included an article called “Car Bombs Inside America,” which had detailed instructions for building such a device at home. “This type of car bomb is used to kill individuals and NOT to destroy buildings. Therefore, look for a dense crowd.” The objective was “maximum carnage” in order to “strike terror into the hearts of the enemies of Allah.”

According to Marquez, he and Farook came up with two maximum-carnage plans in 2011. One was to throw pipe bombs into a crowded cafeteria at Riverside City College, where each of them had studied at different times. The cafeteria had a second-floor balcony. They could attack from above and then escape. The other idea was to hit a local freeway, State Route 91, at rush hour. They chose a stretch of highway west of Riverside. It had hills on the south side and no exits. First, Farook would halt the eastbound traffic with pipe bombs. Then he would walk down the line of cars, shooting trapped motorists where they sat. Marquez, stationed on a hill with a sniper rifle, would pick off police officers as they arrived, and then emergency workers. Marquez, who was nineteen, bought two semiautomatic rifles. (They were concerned that Farook’s South Asian looks might arouse suspicion.) Farook reimbursed Marquez. Marquez also bought smokeless powder for the pipe bombs, and Farook bought two handguns. All legal. They started practicing at local shooting ranges.

It felt cool, I’m guessing, to have this bloody-minded project. Things looked peaceful, normal, banal. Nobody suspected what was coming. Divine vengeance. Their little corner of Riverside—ranch houses, pickup trucks, the Sonic (“America’s Drive-in”) at the corner, the Macy’s and Cheesecake Factory down by 91, certainly those self-involved, blithely sinful college students, with all their partying—had no clue. The two young warriors would smite the necks of the infidels, as the Koran said. It would be a crushing defeat for the enemies of Allah. Farook had become extremely devout. He went to mosque before dawn every day, and again every night, for last prayers. Marquez was more easygoing. He couldn’t match his friend’s level of zeal.

Then Marquez got cold feet. In November, 2012, a federal terrorism bust went down in Chino, only twenty miles away. Four men were arrested. One was from Riverside. The men had met at a mosque in Pomona. Their plan, allegedly, was to travel to Afghanistan to join the Taliban and, eventually, Al Qaeda, to kill American soldiers. The ringleader was an Afghan who had served in the U.S. military. He had used Awlaki videos to help recruit the others, who included a Mexican immigrant and a Filipino immigrant. (The group also included a confidential informant for the F.B.I.) Two of the suspects quickly began coöperating with prosecutors, hoping for lighter sentences. The other two were looking at twenty-five years, possibly more. Somehow this news slapped Marquez awake. He saw his own future, best case. He backed out of the massacre plans with Farook. They stopped hanging out.

Three years later, Marquez was working as a security guard at Walmart. Still living at home, still no girlfriend. He had stopped going to mosque. Now he wanted to join the Navy, but for that he needed to lose weight. He started biking, and hiking. He rode his bike to a part-time job at a dive bar called Morgan’s Tavern. Punk bands played there on weekends. Marquez got into punk, and made some new friends. One of his new friends told me, “He was just a lost young adult. A lot of people are.” He told her about being a Muslim. “It was something he tried out,” she said. She had been in the Army and done a tour in Afghanistan, so she was not unfamiliar with Islam. “Enrique was definitely not into it anymore,” she said. “But he wasn’t really out about his de-conversion. I mean, not to his Muslim friends.” She meant Farook and his family. None of these disparate local scenes struck her as mutually exclusive. She was an atheist hiker. “A lot of people in the punk scene here, they end up going to the military,” she said. “Most places, those two things don’t go hand in hand.”

Marquez was drinking, sometimes heavily, at Morgan’s. Another bar patron later told a Times reporter that when Marquez was drunk he would say things like “There’s so many sleeper cells.” Nobody believed him, of course. He was a goofy kid, eager to be liked, not remotely tough.

On December 2nd, Marquez panicked. He called 911 the next day, suicidal. The operator asked him, “What’s going on?”

“I don’t know. My neighbor. He did the San Bernardino shooting.”

The operator asked, “Your neighbor was in the San Bernardino shooting? He died or what? He was the shooter or what?”

“He was the shooter.”

“He was the shooter?”

Marquez said, “The fucking asshole used my gun in the shooting.”

“You said he used your gun?”

“Yes. Oh my God.”

Marquez tried to explain that he had given his neighbor the gun for safekeeping.

“You had him store your gun?”

“Yeah. And then he. . . .Why did he have to do it?”

“What was the guy’s name that had your gun?”

“Syed Farook.”

Later that day, Marquez drank nine beers and found his way to a hospital emergency room, where he was placed on involuntary hold in a psychiatric ward. He was not arrested, but on December 6th he started talking to the F.B.I. He declined to call a lawyer, and he talked for ten days. He is the sole source for the story of his terrorist partnership with Farook. (Actually, the version we have is the F.B.I.’s version of his tale.) After Marquez finished talking, he was arrested. He was charged with multiple felonies, including providing material support to terrorists, and denied bail.

At Morgan’s, a manager told me, “He thought he’d be safer in there. He don’t want no fourteen families coming after him. He knew he couldn’t survive that.”

There were three Syed Farooks in the immediate family. The father, Syed, Sr., was not a mosquegoer, though he often wore traditional Pakistani shalwar kameez. He had a degree in mechanical engineering but worked as a truck driver. The family had financial troubles, filing for bankruptcy in 2002, and barely avoiding foreclosure on the Tomlinson Avenue house. The elder Syed was often unemployed, and, in 2006, his wife, Rafia, filed for divorce, accusing him in court papers of being physically abusive, “irresponsible, negligent, and an alcoholic.” He sometimes threatened suicide, Rafia said. Syed, Sr., denied the accusations. The family split after an argument, he said, about the historical figure of Jesus. His younger son—known by his middle name, Rizwan—sided with his mother, calling his father “an unbeliever.” Rizwan’s mother was more religious, more conservative than his father. His father had chided him, to no effect, to enjoy his youth more—make friends, go to parties. Rizwan replied that a good Muslim saw only one woman dance: his wife.

A separation agreement stipulated that Rizwan, who was nineteen at the time, must supervise visits between his father and his younger sister. His older brother, Syed Raheel, was by then in the Navy, serving as an information technician on the aircraft carrier U.S.S. Enterprise, where he received, among other awards, the Global War on Terrorism Expeditionary Medal and the Global War on Terrorism Service Medal. Raheel was gregarious. He left the Navy in 2007, got a job monitoring business-tax compliance for the State of California, and married a Russian beautician, Tatiana Chernykh, whose parents live in Israel. Photographs show the couple in Cancún, at Disneyland, and at the beach, with Tatiana, who is blond and attractive, in a bikini. They soon had their first child. The elder Syed lived with them.

Rizwan, meanwhile, looked for a wife on Muslim dating sites based in South Asia and the Middle East. On Dubaimatrimonial.com, he described himself as coming from a “religious but modern family” whose values were an “Eastern and Western mix.” He was six feet tall, he reported, with a “wheatish” complexion; on another site, he wrote that he enjoyed “working on vintage and modern cars” and reading about religion, and liked to “just hang out in back yard doing target practice with younger sister and friends.” Later, on BestMuslim.com, he sounded more devout. “I spend much of my free time in the masjid memorizing the Quran,” he wrote. And: “I am looking for a practicing muslimah, someone who takes her religion very seriously and is always trying to improve her religion and encouraging others to do the same using hikmah and not harshness.” Hikmah is Arabic for “wisdom.”

Tashfeen Malik replied. She seemed to fill the bill. She had finished her pharmacology degree and was studying the Koran at a conservative madrassa in Multan, Pakistan. She and Rizwan e-mailed. They agreed to meet in Mecca, Saudi Arabia, in October, 2013. He would be making his hajj pilgrimage—the spiritual summit, traditionally, of a Muslim life. Her parents, who lived in Riyadh, would bring her to Mecca. According to an “Intention to Marry Statement” that Farook submitted three months later in a U.S. visa petition for Malik, they met for the first time at the home of a relative of hers in Mecca, and were engaged the same day. His petition statement suggested that his parents were present—“my parents and I decided to perform the Hajj . . . we decided to have both of our families meet.” In the end, he travelled only with his mother. With the visa granted, he returned to Saudi Arabia in 2014, and the couple arrived in the United States in July.

Mustafa Kuko remembers their wedding reception. Kuko is the director of the Islamic Center of Riverside, the mosque where Rizwan prayed in the morning and in the evening. Rizwan came to him for advice. “How to pray,” Kuko said. “And how Islam views the marital relation. Many young men come and ask me to help them find wives. We try to help them. Mr. Rizwan didn’t tell me how he got to know his wife, but I told him to double-check on her family background before he made a decision. He went to hajj in 2013 to meet her. Then he came back and asked to have his wedding reception here.” We were talking in Kuko’s small office at the mosque, on a sun-drenched December morning. There were civic awards on the walls—plaques from a Catholic high school and the Loyal Knights of the Round Table, Redlands chapter—along with a banner: “There is no God but Allah, Muhammad is the Messenger of Allah.” Kuko, who was born and raised in Sudan, came to Riverside in 1978. He said that the memorable thing about Rizwan’s wedding reception, which was held after Friday-evening services, was the people he didn’t meet. “I never met his wife. I never met his father. He introduced me to no one. That’s very unusual.”

The Islamic Center of Riverside is large and well appointed. More than a thousand people show up for certain prayers—roughly half of them South Asian by extraction, Kuko said, and half Middle Eastern. Mostly Sunnis, but also Shiites. “It’s a very moderate, passive community,” Kuko said. “Barely connected to religion, really. Between mild and minimal, I would say. They come on Fridays, and after services immediately disappear. Everybody is doing their own thing—their business, their profession. Everybody is looking for the American Dream. We’re very careful that our children are in school, not in jails, and we’re doing very well in that regard.” Kuko, who received a Ph.D. from the University of California, has four American-born children, all grown and thriving. He is white-haired, lean, deeply courteous. Unprompted, he said, in a strained voice, “Why did he do it? It’s beyond me.”

The main problem that Muslim families bring to him constantly, he said, is that the children are too independent, too American. They don’t obey their parents, who are shocked. When they were kids, in the old country, disobedience was not an option. I asked if he saw many young people who were more religious than their parents. He thought about it. “No,” he said. “Only Rizwan.”

But Rizwan’s increasingly intense identification with Islam, and the conflicts that came with it, undoubtedly resonated with Kuko. He himself grew up amid religious-political battles in Khartoum, as Islamists clashed with Communists, and he later lived in Saudi Arabia. He lectures widely on Islam in America. “America has a different brand of Islam,” he told me. “We cannot be Jamaat-e-Islami or Muslim Brotherhood”—major Islamist groups, based in Pakistan and Egypt, respectively. “We are American Muslims. We have to formulate our own ideas that fit with the society we are in. This is not a Muslim country. Our children should learn the public-school curriculum. And then also Muslim history and Arabic.”

It’s a pluralist, assimilationist message, and the greatest pressure on it now is coming not just from nativist politicians but from young Muslims, some of them American-born. Kuko mentioned two young men in Orange County, which is near Riverside, who were recently arrested by the F.B.I.; they were trying to join the Islamic State. One is from a Palestinian family. The other is Sudanese. The Sudanese family had asked him to visit their son in jail. “They fear he is losing his mind,” Kuko said. He sounded weary.

Rizwan switched mosques after he got married, and Kuko never saw him again. He began praying at the Dar Al Uloom Al Islamiyah mosque, a more modest, obscure venue, in the semi-rural flatlands of northwest San Bernardino. Each time I visited Dar Al Uloom, an elderly Pakistani man with a huge orange beard opened the doors for afternoon and evening prayers. He gave his name as Sultana. “Shaitan is the Devil,” he told me. “He wants us to take it easy. Not to pray. Do the bad things. Allah keeps sending prophets to correct people. A hundred and twenty-four thousand. Last one was Muhammad. Whoever prays gets more reward.”

This was not the Islamic Center of Riverside. A few men turned up for prayers. The imam at Dar Al Uloom, Roshan Zamir Abbassi, was elusive, unavailable. Dar Al Uloom had issued, on its Facebook page, a declaration of sadness and solidarity with the victims on the day of the December 2nd attack, but the mosque had received harsh press treatment.

Two young men with full beards, learning that I was a reporter from New York, asked me how they could correct mistakes in an article in the Times. I had a look on someone’s phone. The article was actually in the Post, and it challenged Abbassi’s claims that he barely knew Syed Rizwan Farook. Phone records showed otherwise, according to the Post. The story also connected the mosque to Anwar al-Awlaki, through Abbassi’s brother, who teaches English at a San Diego mosque where Awlaki was once the imam. Finally, it connected the mosque to Tablighi Jamaat, a Sunni revivalist movement that Al Qaeda has sometimes used as a cover to recruit new members.

“We don’t know these people,” one of the young men said, indignant. He gave his name as Hameed. He said he had only seen Rizwan come and go to prayers. Rizwan’s wife, somebody said, stayed in the car, and was veiled.

An argument broke out, only some of it in English, among several men. I got the gist. A middle-aged man in a button-down shirt, whose English was fluent, was berating the young men for being defensive and parochial. Afterward, the older man told me, “How do they expect to be accepted, with their beards growing in every direction? They think they are still in Pakistan. We are in the West.” He was originally from Lebanon. He showed me, on his phone, a library of Biblical texts that included the entire New Testament. He was ecumenical, he said. He studied all religions.

Tashfeen Malik normally wore a niqab—the face veil, leaving only the eyes visible. After her death, Rizwan’s male relatives said that they had never seen her face or heard her voice. Her extended family in Pakistan belongs to a Sufi-influenced branch of Islam, which takes a relatively moderate view of relations between the sexes, but she had embraced the Wahhabist severity of the ruling tribes in Saudi Arabia. Even at the conservative madrassa in Multan, she was notable for wearing the niqab, and for urging others to become better Muslims. They called her “the Saudi girl.” She was active on social media, and the F.B.I. has found at least two private messages on Facebook that she sent, before coming to the U.S., to friends in Pakistan expressing, in Urdu, her support for Islamic jihad and her wish to join the fight.

In California, Malik declined to drive a car. She and Rizwan rented a town house in Redlands, a placid, leafy city ten miles east of downtown San Bernardino. Malik seems to have spent nearly all her time indoors. She remained active online, creating a pseudonymous Facebook page she called Larki Zaat—Urdu for “girl with no name.” Her profile picture was a goat, and one of her first posts from the United States, in August, 2014, was simply, “Woe to coconut muslims.” The reference was to Muslims who were, by her lights, insufficiently militant. It’s a popular slur among ISIS recruits.

I n Joan Didion’s 1966 essay “Some Dreamers of the Golden Dream,” the San Bernardino Valley is “the country of the teased hair and the Capris and the girls for whom all life’s promise comes down to a waltz-length white wedding dress and the birth of a Kimberly or a Sherry or a Debbi.” The neighborhood has changed since 1966. Millions of people have moved to Riverside and San Bernardino counties in search of affordable housing. Their names are more likely to be Pedro or Tatiana than Debbi. The urbanized area, now known as the Inland Empire, has quadrupled in population, to more than four million, with roughly a million first-generation immigrants, speaking dozens of different languages. The region has no discernible center. It is a continuous mass of old and new, seemingly overlapping towns and city-size suburbs, all knitted together by freeways. Karthick Ramakrishnan, a professor of public policy at the University of California Riverside, notes that religious institutions figure more prominently in the Inland Empire than in the coastal conurbations—Los Angeles, the San Francisco Bay Area. Indeed, churchgoing is so pervasive that it drains energy from other forms of civic involvement. Mormons, Catholics, mainline Protestants, Seventh-Day Adventists, and seemingly every stripe of evangelical Christian fill the local churches. Muslims, Hindus, and Buddhists are all amply represented as well.

Makeshift memorials sprang up along South Waterman Avenue, in San Bernardino, after the December 2nd massacre, which occurred in a conference room at a complex called the Inland Regional Center, on South Waterman, a mile north of Interstate 10. The center, a community-based nonprofit, serves people with developmental disabilities. The county health department had reserved the conference room for a training session (“Ready to be bored?” a colleague muttered to Syed Rizwan Farook, before he ducked out), to be followed by a party. After the shooting, the complex was closed and was surrounded by a chain-link fence with green netting. The largest of the spontaneous memorials grew at the corner of South Waterman and East Orange Show Road. There were flowers, flags, candles, Christmas trees, wreaths, and hundreds of fervent notes. There was a banner for Aurora Godoy, the youngest of the dead. She was twenty-six. The banner carried a photograph of her with her husband and baby. A thousand people went to Godoy’s funeral. Isaac Amanios, an immigrant from Eritrea, was the oldest of the dead. He was sixty. A California state flag shivered in the wind. The flag had been signed by dozens of people, including Vicky and Juan C, Indio, CA. “Tucson Stands with San Bernardino.” There were wooden stars from Massapequa and Breezy Point, New York. Quotes from the Bible were taped up. “Believe on the Lord Jesus Christ and Thou Shalt Be Saved.” The Khmer Buddhist Society of San Bernardino offered its condolences, as did Indian Springs High School.

How did Tashfeen Malik understand her new, ultra-diverse, thoroughly American surroundings? When she got pregnant, she registered online at Target for baby items, or maybe Rizwan did it—or his mother, who sold the house on Tomlinson Avenue and moved in with them in the rented town house—but the account was in Malik’s name. Diapers, swabs, a car seat. Rizwan’s colleagues at the health department, who never met Malik, held a baby shower. After his daughter’s birth, in May, he took paternity leave.

Malik received a conditional green card in July. She didn’t speak to the neighbors. Presumably, everything beyond her doorstep was haram—forbidden. Like all places not ruled by Islam, America was Dar Al-Kufr (the territory of disbelief) or, possibly, Dar Al-Harb (the territory of war). The couple’s landlord, Doyle Miller, an eighty-one-year-old white man, told reporters, “She did not like to be seen. She did not seem to like people around here. He seemed ordinary, no worries for me at all. I’m only now thinking that maybe she wore the pants. It could be that she was behind it all.” Rizwan, if Enrique Marquez is to be believed, had harbored carnage fantasies for years. He already had the weapons. Now, it seemed, he had a truly willing partner. Indeed, it has been suggested (by the F.B.I., by Jennifer Thalasinos) that he figured in Malik’s plans even more than she figured in his. They were stockpiling ammunition and, in the garage behind the town house, building pipe bombs according to a recipe they found in Inspire.

And their infant daughter? A psychiatrist would say that the parents must not have formed a normal bond with their child. But what is normalcy when the prospect of holy martyrdom beckons, when disgust with the fallen world, the enemy’s world, is so chokingly thick that you are willing to gun down ordinary people as if they were evil ghosts? In the death cult of apocalyptic jihad, the final battle between the righteous and the wicked is nearly at hand. The Islamic State trades extensively in end-times ideology. It was to Abu Bakr al-Baghdadi, the leader of the Islamic State, the self-appointed caliph, that Malik dedicated her bay’ah—her pledge of allegiance—on Facebook after she and Rizwan fled the site of the attack. The Islamic State seemed not to know who these two mass murderers were but soon enough declared them “soldiers of the caliphate” and asked God to accept them as martyrs.

Although the operation appeared ill-planned, there was some evidence of forethought. Malik and Farook rented a black Ford Expedition with Utah plates, which might delay identification during a getaway. They smashed and discarded phones and computer drives. But they did not attack a school or a concert or a gridlocked freeway. Instead, they attacked a room full of people who knew Farook, and who recognized him despite the ski mask he was wearing. There are differing accounts of the murder scene. In one, Farook had left the party angry after an argument and then come back, half an hour later, armed. In another, the attackers were three white men. In a third, published by the Sunday Times of London, and attributed to “witnesses,” it was Malik who fired first, “aiming semiautomatic fire at people gathered around a Christmas tree, knocking it sideways.” At her side, “Farook appeared to hesitate, perhaps momentarily losing his nerve or maybe to seek out a specific victim, such as Thalasinos.”

People fled deeper into the building, that was certain. Ceiling sprinklers were set off by the gunfire. The shooters emptied four thirty-round magazines, striking thirty-six people and killing fourteen, and then immediately fled, although they were wearing vests packed with more ammunition. They left a bag with three pipe bombs on a table—the remote-control detonator was in their vehicle—but the bombs failed to explode, perhaps because of the sprinklers.

Then they spent four hours driving, in no discernible pattern, around Greater San Bernardino. You have to wonder what they talked about. They normally communicated, apparently, in English—hers labored, his fluent. They did not appear to have a second act planned—neither another attack nor an escape or a suicide mission. At 2:56 p.m., they drove slowly past their town house on North Center Street, in Redlands. Their daughter was inside, with her grandmother. The police were outside, in unmarked cars. The chase began, with Farook driving and Malik firing from the back seat, blowing out the vehicle’s rear window.

On Christmas Eve, I watched the light slowly fade on North Center Street. The front door and windows of Farook and Malik’s place were boarded up. It was a crisp afternoon. Well-dressed grandmothers carried wrapped presents from houses to cars and drove off. Excited kids ran giggling to wreathed doorways and were ushered in. The wide, quiet street was lined with palm trees, pine trees, sycamore, eucalyptus. A mailman wheeled his cart, blue canvas bag sagging, from door to door. I tried to imagine all this as Dar Al-Kufr. Three teen-agers walking by paused, staring at the boarded-up town house. “Oh,” one said. Another took a photo with a phone. “Why is there an American flag?” the third kid asked, as they walked away. The adjoining town houses each had American flags on poles, and Christmas decorations: little sparkling stars, wooden signs saying “Joy*”* and “Noel.” At the bottom of a window, two passages from Scripture were taped to the glass. From Psalms: “The Lord is near to the broken-hearted, and saves those who are crushed in spirit.” From Timothy: “For God gave us a spirit not of fear but of power and love and self-control.”

A few days after the attack, Syed, Sr., who still lives with his son Raheel, gave a doorstep interview to the Italian paper La Stampa. He called Rizwan a “mama’s boy.” He also called him an “angel.” He told the story of the family argument about Jesus, and Rizwan’s calling him an unbeliever. He said that Rizwan had been obsessed with Israel and once told him that he shared the ideology of Baghdadi and the Islamic State. Later, he said he did not remember saying these things to the Italian reporter. But the transcript of their conversation rings true. Syed, Sr., laments the end of his marriage and the loss of his house: “I bought a beautiful house and planted twenty fruit trees in the garden. They sold the house and destroyed my family.” His son’s marriage to the reclusive Malik was another disaster. “I told my son that it was destroying our family, but he didn’t care.” The young couple’s final rampage was a devastating mystery to him. “I despair and I do not understand.” Syed, Sr., sounded ready to return to Pakistan. “My life here is over,” he said. But the F.B.I. has placed him and his ex-wife on the terrorist no-fly list.

The day before his death, Nicholas Thalasinos reported on Facebook that he had received an online threat saying he would “die and never see Israel.” The message was not, as some assumed, from Malik or Syed Rizwan Farook. Thalasinos led a disputatious life on Twitter and Facebook, writing with a vehemence that is normally reserved for comments posted anonymously, or pseudonymously. Thalasinos wrote under his own name, under photos of himself and his wife. He was sometimes barred from posting—placed in what’s known as “Facebook jail,” with his account temporarily disabled, for violating the company’s standards concerning hate speech—and during those periods he used the name Michael Thalasinos to continue posting. He berated, often several times a day, liberals, Democrats, terrorists, Iran, ISIS, Planned Parenthood, President Obama, Michelle Obama, gun control, and Muslims.

It was his rage against Muslims that drew the threats and the bans. On October 30th, he tweeted, “Islam—the CULT of RAPE, PEDOPHILIA, ANTISEMITISM and MURDER.” He posted a banner describing the Koran as a “training book for terrorism.” He applauded the destruction of mosques and advocated that the United States “nuke” Iran and ISIS. In 2013, Thalasinos wrote, “IF Islams Allah exists AT ALL—it could just be the fantasy of a STONED ANTISEMiTIC PEDOPHILE named Muhammad for all I know . . .” He called Palestinians “FAKESTINIANS.” His comments about Obama, whom he believed to be a Muslim supremacist who secretly supported ISIS, were no more temperate. To those who advocated lynching the President, he replied that, because he believed in the Constitution, he would prefer to see Obama tried for treason and executed. Two days before he died, Thalasinos wrote, “Now our President MAKES DEALS WITH HaSatan that gives Iran TIME, MONEY, and GUARANTEED PROTECTION so they can BUILD NUCLEAR WEAPONS and do what OBAMA (the UTTERLY VILE PAGAN FILTHY ANTISEMITIC DRUG ADDICTED MAGGOT that he is) PROBABLY DREAMS OF DOING EVERY DAY—NUKING ISRAEl!”

Many people unfurl a ferocious doppelgänger online. Aggressive speech is legal and categorically different from acts of violence. What is eerie about the preoccupations and fury of Thalasinos is how, in retrospect, they foretell the terrible end of his life. He wrote regularly about jihadist terror attacks in the U.S.—September 11th, Fort Hood, the Boston Marathon—and about workplace violence. He wrote a long post about a Muslim in Oklahoma who threatened to behead a co-worker, under the headline “ARE YOU AWAKE YET AMERICA?” He heaped scorn on the possibility that incidents he considered jihadist attacks might be dismissed as workplace violence. He celebrated guns, posting pictures of women with pistols tucked under their bras or rifles slung across their hips, and singled out the AR-15 rifle—“Hold on to your AR-15s.” Malik and Farook used AR-15-style rifles on December 2nd. Thalasinos even posted a picture of a goat’s-head symbol sewn on a sneaker, intending to show that Satan is making his way everywhere. The symbol looked, at least to me, like Tashfeen Malik’s profile picture on her Facebook page.

Were Malik and Farook following the sulfurous posts and tweets of Thalasinos? The killers tried to erase their electronic footprints. If the F.B.I. has reconstructed their browsing history, it has not said so. When you read what Thalasinos wrote, it is difficult, in any case, not to picture the colleague with whom he argued about religion reading the same inflammatory invective. Malik, the postpartum shut-in—Jennifer Thalasinos called her a “mail-order bride for ISIS”—would have been, I imagine, even more appalled and implacable.

The world has 1.6 billion Muslims. Jihadists are a tiny minority, but for now they are the unavoidable topic. As the British Muslim reformer (and ex-Islamist) Maajid Nawaz says, “They dominate the discourse because they’re violent.” Some jihadist groups are regional. Some, like the Islamic State, are global. Jihadism did not emerge from a vacuum. Its adherents have chosen the revolutionary path of direct action, but they operate with a disturbing amount of passive support from other, less motivated Muslims.

Killing Osama bin Laden and Anwar al-Awlaki—even defeating the Islamic State militarily, essential as that may be—will not stop the ideology, or reverse its growth. Terror is jihadism’s most frightening weapon but not its core. Its ideas, which can be summed up as Muslim supremacism, are its greatest strength. These ideas are righteous, utopian, salvific. They promise to relieve an enormous experience of impotence and humiliation. Even to certain young Westerners, living in comfort and freedom, with no credible personal grievances, they seem to offer an exciting counterculture. The world is ending, and it is ending in blood. Choose Paradise.

The investigation into the San Bernardino massacre appears to be largely focussed on the question of whether the shooters belonged to a network. If they did, it’s important to try to roll it up. But at the moment it looks as if they carried out their plan and achieved their pitiless martyrdom without the support of a group.

There were more terrorism arrests—fifty-six—in the United States in 2015 than in any other year since 2001. Last fall, James Comey, the director of the F.B.I., said that the bureau was pursuing nine hundred active investigations, in all fifty states, against homegrown violent extremists, most of them connected to ISIS. Hundreds of Americans—and thousands of Europeans—have made their way to Syria and Iraq to join the fighting for the so-called caliphate. But now ISIS is asking its supporters, as Al Qaeda did before it, to stay home and stage attacks where they are, particularly in the Dar Al-Kufr. The goal is to provoke crackdowns and divisions—within the West, between Muslims and the West, between different groups of Muslims. The strategy is working. ♦

William Finnegan has been a contributor to The New Yorker since 1984 and a staff writer since 1987. He is the author of “Barbarian Days.”